1. Field Of The Invention
The present invention relates to a process for preparing monochlorinated hydrocarbons which bear an alkyl radical having from 3 to 20 carbon atoms to which the chlorine atom is bound. In the process, appropriate alcohols are reacted with cyanuric chloride and the reaction mixture is subsequently worked-up.
2. Discussion Of The Background
Monochlorinated hydrocarbons such as alkyl chlorides are, inter alia, valuable as intermediates for the preparation of crop protection agents and pharmaceutical products. They are therefore often required in a high isomeric purity.
The preparation of monochlorinated hydrocarbons such as alkyl chlorides generally starts from olefins or alcohols.
Methods of preparing isomerically pure alkyl chlorides are known and described in the literature. S. R. Sandler, J. Org. Chem. 35, 3967 (1970), describes the conversion of primary, secondary and tertiary alcohols into alkyl chloride compounds by reacting the alcohols with an excess of cyanuric chloride under anhydrous conditions. Furthermore, on page 3968 of the text, the reaction of 2-pentanol with cyanuric chloride, zinc chloride/hydrogen chloride, thionyl chloride/pyridine and with hydrogen chloride is described. Isomerically pure 2-chloro-pentane is obtained in a yield of 48% in the reaction with thionyl chloride/pyridine and in a yield of 57% in the reaction with cyanuric chloride alone.
Disadvantages of these processes are, in particular,
a) that a residual amount of cyanuric chloride remains in the crude monochlorinated hydrocarbon after the solids (cyanuric chloride, cyanuric acid and derivatives) have been separated and there is considerable sublimate formation in the work-up by distillation,
b) that very long reaction times are sometimes required when the number of carbon atoms in the hydrocarbon portion of the molecule increases, and
c) that large amounts of toxic pyridine have to be handled and pyridine hydrochloride is formed in large amounts when using thionyl chloride/pyridine. A need continues to exist for an improved method of producing isomerically pure monochlorinated hydrocarbons in high space time yield.
Accordingly, one object of the present invention is to provide a simple process by means of which isomerically pure monochlorinated hydrocarbons, which contain an alkyl radical having from 3 to 20 carbon atoms to which the chlorine atom is bound and to which additional hydrocarbon radicals may be bound, can be prepared in high space-time yields.
Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by reacting a monoalcohol with cyanuric chloride with or without addition of a phase transfer catalyst (PTC) and then purifying the resulting mono-chlorinated hydrocarbon by distillation after mechanical removal of salts and washing of the product with alkali.